A planetary gear bearing system is typically used in a planetary gearset. A planetary gearset of this type typically includes at least one sun wheel, an annulus wheel and a planet carrier, on which at least one planet wheel is rotatably mounted on a bearing axis. The sun wheel drives, for example, the planet wheel, at least multiple, for example three, planet wheels being distributed equidistantly, which are driven together via the sun wheel. The planet wheel(s) mesh(es) with the annulus wheel, so that the corresponding gear ratio occurs.
Methods are known for rotatably mounting the planet wheel on the bearing axis via a friction bearing. Rolling bearings are typically used for mounting. In large planetary gearsets, in particular, the use of a hydrodynamic bearing is known, which is lubricated with the aid of a corresponding lubricant, for example oil. Under high loads and at low relative speeds, the friction partners of the friction bearing move in so-called mixed friction mode. In this case, the rotating friction partner is not completely carried by the intermediate lubricating film, but instead an, at least partial, surface contact exists between the rotating friction partner and the counter-rotating partner.
In general, the friction partner carrying the circumferential load, i.e., generally the rotating shaft, should have a greater hardness, possibly a surface hardness, than the counter-rotating partner. Based on this design, the surface contour of the counter-rotating partner adapts to the contour of the friction partner, which is generally designed as a shaft. After initial run-in wear, this contour adaptation effectuates a reduced wear by reducing the mixed friction portion or shifting of the mixed-friction area toward lower rotational speeds. The run-in phase is absolutely necessary for friction bearings such as those used here. During hydrodynamic operation, however, the one friction partner of the friction bearing is carried entirely by the lubricating film. It is separated from the counter-rotating partner by this lubricating film. Compared to the mixed-friction state, the hydrodynamic state occurs at higher relative speeds (constant pressure) or lower pressures (constant relative speed).
In principle, an operation in the mixed-friction state would be advantageous, since the minimum value of the Stribeck curve is in this range, which describes the curve of the friction force or the friction coefficient as a function of the friction velocity in the case of a hydrodynamic friction. Starting from the minimum value of the Stribeck curve, the friction force increases again at higher friction velocities, due to the increasing intensity of the liquid friction, even if a transition to sliding friction occurs.
The gearing of the planet wheel and the annulus wheel gearing meshing therewith is usually a helical gearing. For this reason, an axial load also acts upon the friction bearing, which induces a tilting moment. This means that an edge pressure occurs in the friction bearing area, which is conducive to wear. This is all the more true since, in known friction bearing systems, one friction partner of the friction bearing material pairing is provided with or includes a surface layer made of white metal or bronze, while the other friction partner of the material pairing has a surface made of unhardened or hardened steel or a hard chrome-plated surface. If an uneven introduction of force occurs, due to operation, and a tilting moment results as a consequence, this stresses, in particular the friction partner made of white metal or bronze, since it is the softer friction partner within the material pairing and is therefore more susceptible to wear. If the planetary gearset has a large design, as is generally the case in gearsets which are used in the area of wind turbines, considerable tilting moments result, which are conducive to wear. In large planetary gearsets, in particular, this is problematic, since a worn bearing component may not be readily replaced, or if this is possible at all, only with a great deal of effort.